The chemokine receptor gene CCR5 plays an important role in many immune-related processes. Delta 32 rs333, designating the CCR5-delta32 deletion of 32 nucleotides from within the gene, is perhaps the most famous allele of CCR5. 23andMe tests for this under their private identifier/name, I3003626.

Individuals carrying one copy of the delta 32 allele are somewhat resistant to infection by HIV, the virus that causes AIDS, and individuals with 2 copies (delta 32 homozygotes, ~1% of Caucasians) are almost completely immune to infection by HIV. [PMID 8898752] The delta 32 allele may have been selected for in European populations because it confers resistance to plague (Black Death) or smallpox. [1]

[PMID 16216086] shows the the geographic spread of the allele. [[Image:Journal.pbio.0030339.g001.png|thumb|300px|The geographic spread of the allele [PMID 16216086]]]

Does the CCR5-delta32 mutation have an entirely positive/protective role?

Probably not. In patients with abdominal aortic aneurysm (AAA), the major risk is a sudden rupture - which is quite often fatal. Individuals with the delta 32 variant are more likely to have aneurysms than non-carriers, and among patients with aneurysms, delta 32 carriers are more likely to rupture than to be diagnosed in time for surgical repair. [PMID 15557916]

Tests for CCR-delta32 are offered by FamilyTreeDNA (FAQ), 23andMe, and possibly other direct-to-consumer genetics testing companies.

[PMID 15726497] Gene-environment interaction effects on the development of immune responses in the 1st year of life.